NEWTONS' LAW OF MOTION - Electrical4u

NEWTONS' LAW OF MOTION 

FORCE 

• a pull or push which changes or tends to change the state of rest or of uniform motion or direction of motion of any object is called force. 
• it is a vector quantity.

EFFECT ON RESULTANT FORCE 

1. May change only direction of motion 
2. May change only speed 
3.  may change size and shape of body 
4.  may change both speed and direction of motion 

Unit of force 

• Newton and (kg.m)/s^2  (in MKS system)
• Dyne and (g.cm)/s^2  (in C.G.S system)
• 1 newton = 10^5 dyne 

• Dimensional formula of force = [MLT^-2]

ELECTROMEGANATIC FORCE 

• Force exerted by one particle on the other becouse of the electric charge on the particles is called Electromeganatic force 

Characterestics of electromegnatics force 

1.  these can be attractive or repulsive 
2.  these are long range force
3.  depends on nature of medium 
4.  all macroscopic force ( except gravation ) which we experiences as puss or pull or by all contact are electromagenatic 

NUCLEARE FORCE 

• it is the strongest force , it keeps nucleons neutrons and protons together inside the nucleus inspite of large electric repulsion between protons . Radioactivity , fission , and fusion , etc . result becouse of unbalancing of nuclear force . it acts within the nucler that too upon a very small distance .

Classification of force on the basis of contact

• Field Force - Forces which acts on an object at a distance by the interaction of the object with the field produced by other object is called field force 
• examples - Gravitiation force , Electromagnetic force 

• Contact force - which forces are transmitted between bodies by short range molecular interaction are called contact forces . when two object comes in contact they exert contact forces on each others. 

TENSION 

• Tension in a string is a electromagnatic force . it arrises when a strings is pulled . if a massless string is not pulled . tension in it is zero . A string suspanded by rigid support is pulled by a force 'F' .

• T = F 

Frictional force  - it is component of contact force tangential to the surcface . it opposes the relative motion of the two surface in contact.

NEWTONS' LAW OF MOTION 

• First law of motion :- Every body preserves inits state of rest , or of uniforms motion in a right line , unless it is compalled to change that state by forces impressed thereon . 

• Every body continues to be in its state of rest or of uniform motion in a straight line unless compelled by somone external force to act otherwise . 

• Newton's first law is really a statement about refrence filames in that it defines the type of refrence frames in which the laws of newtonian hold . 

example of First law of motion 

1.  A bullet fired on a glass windows makes a clean hole through it while a stone breaks the whole of it .
2.  A passenger sitting in a bus gets a jerk when the bus starts or stop suddenly 

Second law of motion :- The rate of change of momentum of a body is proportional to the appiled force and takes place in the direction in which the force acts 

• F = m.a 

where , F = force

        m = mass 

        a = accleration 

Applications of newtons laws 

a) When objects are in equilibrium 

   To solve problems involving objects in Equilibrium 

step 1 : - makes a sketch of the problem

step 2 : - isolate a single object and then draw the free - body diagram . label  all external forces acting on it. 

step 3 : - choose a convenient coordinate system and resolve all forces into X and Y  components . 

step 4 : - Apply the equation {Fx = 0 and { Fy = 0 

step 5 : - find unknown several  quantities 

Third Law of Motion :- To every action , there is always an equal and opposite reaction .

Important point about the Third Law 

1.  the terms 'action' and 'reaction' in the third law means nothing else but 'force' . a simple and clear way of starting the third law is as followed force always in pairs .
2.  the terms 'action' and 'reaction' in the third law may gives a wrong impression that action comes before reaction i.e action is the caused and reaction the effect. there is no  such cause - effect relation implied in the third law . 

SYSTEM 

• Two or more than two objects which intract with each others from a sysrem .

Classifaction of forces the basis of boundary of system:

• Internal force - forces acting each with in a system among its constituents.
• External force - forces exerted on the constituents of a system by the outside surrounding are called as external forces.
• Real force - Force which acts on object due to other object is called as real force . An isilared object does not experience any real force.

FREE BODY DIAGRAM 

• A free body diagram consists of a diagrammatic representation of a single body or a subsystem of bodies isolated from its surroundings showing all the forces acting on it.